Engineers and technicians often have a need to generate various electrical resistances to produce a load or test on an electronic device. This may be accomplished by using a potentiometer or a rheostat. However, in order to operate across a wider range of resistances with more accuracy, it has long been known to use a decade resistance box, in which sets (or “decades”) of resistors are placed in series with each other and independently controlled to allow a wide range of resistances to be precisely provided. Each decade of resistors is able to generate integer multiples of 10x from 0 through 9 or 10, each decade being associated with a different power x. Thus, for example, U.S. Pat. No. 731,209 (Northrup) describes a decade resistance box with five decades (values of x ranging from −1 through 3), each decade having four resistors in series (with resistance values of 10x, 3(10x), 3(10x), and 2(10x)), allowing the user to generate any resistance ranging from 0.1Ω to 9,999.9Ω with a resolution of 0.1Ω by rotating mechanical dials representing the different powers of 10 places. U.S. Pat. No. 4,227,172 describes decades that are made up of four resistors that may be dynamically arranged either in series or parallel or both, also allowing for easy multiplication of a resistance by factors of 10.
Various improved decade boxes utilize electrical switching using transistors, such as, for example, U.S. Pat. Nos. 4,157,494, 4,849,903, and 8,810,354. U.S. Pat. No. 6,487,456 (Masano, et al.) describes a digital input interface used in connection with a microprocessor that allows the resistance of each individual resistor to be calibrated. Masano also teaches using relays to select resistors.